Link Slab Construction [SIG]

This object places one or more link slabs into the construction sequence. It activates a slab's joint constraints at the stage the slab is cast, and applies the slab's own weight from that stage onward.

A link slab is cast into a blockout after the girders are erected and the decks poured, so the girder and deck dead load has already deflected the spans and the slab never sees it. Staging the slab is what preserves that split: without it the joint constraints are live from the first stage, the two spans interact before the slab physically exists, and the dead-load history the design depends on is silently wrong — the model still analyses and still looks correct.

One instance per casting stage is enough. The constraints are added at the named stage and carry forward automatically to later stages.

General

Casting Stage: The construction stage at which these link slabs are cast. Select a stage defined under Construction Stage. The joint constraints become active at this stage and the slab weight is applied from here on; before it, neither exists in the model. A value is required.

Link Slabs: The link slabs cast at this stage, selected from the Link Slab objects in the model. More than one may be listed when several joints are cast in the same pour. At least one entry is required.

Self Weight Factor: Scales the self weight applied for these slabs. The default of 1 applies the weight of the slab exactly as drawn. Raise it to account for anything poured with the slab but not modelled separately — formwork, or a wearing course carried across the joint. Cannot be negative.

How the slab weight is applied

The weight is applied as a surface load over the joint region of the adjacent decks rather than as a structural element. An element raised for the slab's mass would add stiffness at the joint in every analysis case, which is exactly the moment continuity a link slab is designed to prevent. A surface load has no stiffness, so the slab's weight is carried without tying the two spans together.

One consequence worth knowing: the load is distributed to the deck mesh nodes under the joint, so slab concrete lying outboard of the outermost deck gridline has no node to carry it. If that portion matters for your model, raise the Self Weight Factor to compensate.